Department of Geography and Anthropology, Louisiana State University, Baton Rouge, 70803-4105, USA.
Am J Phys Anthropol. 2011 Jul;145(3):426-37. doi: 10.1002/ajpa.21518. Epub 2011 May 3.
Humans do not have a tail, but we have four rudimentary coccygeal vertebrae. This study considers several issues pertaining to fusion of the coccyx to the sacrum, including prevalence, sexual differences, effect on pelvic size, and obstetrical and evolutionary implications. Previous research on sacral-coccygeal fusion has reported: (1) lower prevalence in females than males, (2) prevalence increases with age, (3) range in prevalence among 13 samples from 0 to 72%, and (4) obstetrical complications. This study uses a sample of 2,354 American skeletons of known sex, age 20 years and older to ascertain prevalence of sacral-coccygeal fusion and to evaluate some of its correlates. Results show that the sexes do not differ in prevalence of sacral-coccygeal fusion for five of seven decades of life, but that prevalence does increase with advancing age-from 24 to 47% from the third to eighth decades of life in females. Pelvimetric analysis of 132 females shows that those with sacral-coccygeal fusion have a shorter posterior sagittal diameter of the outlet compared to those without fusion; more than half of those with sacral-coccygeal fusion have an obstetrically contracted posterior sagittal diameter. Shortening of the posterior sagittal diameter is important, because its conjoint occurrence with a narrow subpubic arch may result in an obstetrically inadequate outlet. This study concludes that sacral-coccygeal fusion is a principal contributor to the evolution of sexual dimorphism in sacral angulation, which is a determinant of the length of the posterior sagittal diameter of the outlet.
人类没有尾巴，但我们有四个退化的尾骨。本研究考虑了与尾骨和骶骨融合相关的几个问题，包括融合的普遍性、性别差异、对骨盆大小的影响，以及产科和进化意义。之前关于骶尾骨融合的研究报告：（1）女性的发病率低于男性；（2）发病率随年龄增长而增加；（3）13 个样本的发病率范围为 0 到 72%；（4）产科并发症。本研究使用了已知性别的 2354 具美国骨骼样本，年龄在 20 岁及以上，以确定骶尾骨融合的发病率，并评估其一些相关因素。结果表明，在七个年龄段中，有五个年龄段女性和男性的骶尾骨融合发病率没有差异，但发病率随着年龄的增长而增加——从第三到第八个十年，女性的发病率从 24%增加到 47%。对 132 名女性的骨盆测量分析表明，与没有融合的女性相比，有骶尾骨融合的女性出口的后矢状径较短；超过一半的骶尾骨融合女性的出口后矢状径产科狭窄。后矢状径缩短很重要，因为它与耻骨弓狭窄同时发生可能导致出口产科不足。本研究得出结论，骶尾骨融合是骶骨角度性别二态性进化的主要原因之一，而骶骨角度是出口后矢状径长度的决定因素。
